1. Field of the Invention
The present invention relates to a process for manufacturing a semiconductor device, and more specifically to a method for rinsing and drying a semiconductor substrate, i.e., wafer, that was wet-treated with various chemicals.
2. Description of Related Art
Mass production of a semiconductor device has already entered into the age of the sub-micron, and a weight of development has been shifted into the next stage of a half-micron. With this advanced microfabrication, an ultra-micro foreign matter and a slight stain adhered to a wafer in the process results in a defective wafer, with the result that the importance of a rinsing technology is recognized anew, and elevation of the rinsing performance is desired.
In the Japanese language monthly magazine "Semiconductor World", March, 1995, Press Journal, the special edition entitled "Rinsing - its simplification and reliability" explains the present situation of the rinsing technology.
In the prior art, a wafer etching and rinsing method of a multi-bath process is known. For example, a series of treatments are sequentially executed which fundamentally use an APM (ammonia-hydrogen peroxide mixed water=NH.sub.4 OH/H.sub.2 O.sub.2 /H.sub.2 O), an HPM (hydrochloric acid-hydrogen peroxide mixed water=NCl/H.sub.2 O.sub.2 /H.sub.2 O), and a DHF (diluted hydrofluoric acid=HF/H.sub.2 O), in combination with an SPM (sulfuric acid-hydrogen peroxide mixed water=H.sub.2 SO.sub.4 /H.sub.2 O.sub.2 /H.sub.2 O), a BHF (buffered hydrofluoric acid) and a FPM (hydrofluoric acid-hydrogen peroxide mixed water=HF/H.sub.2 O.sub.2 /H.sub.2 O), if necessary.
FIG. 1 shows one example of the wafer etching and rinsing method in the multi-bath process. In brief, a wafer is mounted on a loader "a", and then is fed to an APM chemicals bath "b", an DHF chemicals bath "d" and an HPM chemicals bath "f", in the named order. In this case, a QDR (quick dump rinse) bath "c", "e" or "g" is located between each pair of adjacent chemicals baths, in order to rinse the wafer with deionized water, thereby to prevent the chemicals from entering into the next downstream chemicals bath.
The wafer delivered from the QDR bath "g" is fed through a rinse bath "h" to a wafer drying chamber "i" of a spin dryer type or an IPA (isopropyl alcohol) vapor drying type. Thereafter, the wafer is fed to an unloader "j".
In the above mentioned multi-bath wafer rinsing and drying method, if the mechanism for circulating and filtering the chemicals is used, it is possible to advantageously reduce the consumed amount of chemicals to a limit within a contamination range sufficiently permitting the use of the chemicals. Since a number of baths are used, the throughput is high in some cases depending upon the process to be performed. However, since the wafer must be delivered in the atmosphere, there is high possibility that dust occurs in the course of delivering the wafer in the atmosphere, and water marks often occur.
There is a single-bath type, which is opposite to the multi-bath type. In this single-bath type, all of a wet etching by chemicals, a rinsing by chemicals, a rinsing by deionized water, and a drying are carried out in a single bath. Accordingly, a liquid must be replaced by another at each time each processing is to be carried out, with the result that the amount of used chemicals becomes large. In addition, the throughput is low. However, since chemical water solution is replaced with another at each processing step, there is less re-contamination due to particles or dirt remaining in the chemical solution. This is the most important advantage of the single bath type. In connection with the cost, the increase of the amount of used chemicals is prevented by adopting a dilution process.
Referring to FIGS. 2A to 2H, explanation will be made on an example of a prior art single bath wet-process utilizing an IPA drying, which is considered to be effective in reducing the particles and the water marks in comparison with the multi-bath type, and which is disclosed by U.S. Pat. No. 5,520,744, to Fujikawa, et. al. content of which is incorporated by reference in its entirety into this application. FIGS. 2A to 2H are diagrammatic sectional views of the single bath wet-treating unit substantially corresponding to that shown in FIG. 6 of U.S. Pat. No. 5,520,744. This single bath wet-treating unit includes a hermetically sealable chamber 402 having a top closed and opened by a hermetically sealable lid 403. Within this hermetically sealable chamber 402, a treating bath 407 is located, and nitrogen or IPA vapor supplying nozzles 404 are mounted at an upper position. The treating bath 407 has deionized water supply nozzles 405 located at a peripheral portion of the bottom, and a discharge port 406 formed at a center of the bottom. In FIGS. 2A to 2H, a pipe layout for supplying necessary liquid and gas and for exhausting unnecessary liquid and gas is omitted for simplification of the drawing.
In the single bath wet-process, first, a wafer 401 is introduced into the treating bath 407 by means of a conveying cassette (not shown) so that the wafer is immersed in deionized water 409 in the treating bath 407. Thereafter, the chamber 402 is closed with the lid 403 so as to complete a hermetically sealed space defined by the chamber 402 and the lid 403, and nitrogen is supplied through the nitrogen or IPA vapor supplying nozzles 404.
In this condition, the deionized water is supplied from the deionized water supplying nozzles 405 so that a rising stream of deionized water is generated. Accordingly, the wafer 401 is put in the rising stream of deionized water for a predetermined period of time, as shown in FIG. 2A. Thus, particles are removed from a surface of the wafer 401, and are exhausted from the treating bath 407 together with the deionized water 409 overflowing from an upper edge of the treating bath 407.
Then, without exposing the wafer 401 to the atmosphere, the deionized water is replaced with a chemical solution, for example, the DHF liquid 410, which is therefore supplied through the nozzles 405 so as to fill the treating bath 407 with the DHF liquid 410. In this condition, an etching is carried out for a predetermined period of time, as shown in FIG. 2B. At this time, the nitrogen is still supplied from the nozzles 404.
Thereafter, without exposing the wafer 401 to the atmosphere, the DHF liquid 410 is replaced with the deionized water, which is therefore supplied through the nozzles 405, and the wafer 401 is rinsed with a rising stream of deionized water 409 for a predetermined period of time. In this process, particles removed from the surface of the wafer 401 and diffused into the deionized water 409, are exhausted from the treating bath 407 together with the deionized water 409 overflowing from the upper edge of the treating bath 407, as shown in FIG. 2C. At this time, the nitrogen is still supplied from the nozzles 404.
When the rinsing of the wafer 401 is completed, as shown in FIG. 2D, a vapor 411 of an organic solvent, for example, IPA, which is soluble to water and which acts in lower the surface tension of the deionized water, is supplied toward an upper position of the treating bath 407 from the nitrogen or IPA vapor supplying nozzles 404, by using the nitrogen gas as a carrier. Thereafter, the wafer 401 is pulled up from the treating bath 407, as shown in FIG. 2E.
In the process described above, since a thin IPA layer 412 is formed on a surface of the deionized water 409, the deionized water on the wafer 401 is replaced with the IPA when the wafer 401 is pulled up, so that the wafer 401 will be dried quickly. Here, the water soluble organic solvent acting to lower the surface tension of deionized water can be exemplified by the alcohol family, the ketone family and the ethyl family, but the IPA is the most preferable because IPA containing a lasser amount of impurities, such as metal, is commercially easily available.
If the pulling-up of the wafer 401 from the deionized water 409 is completed, the supplying of the IPA vapor 411 is stopped, and the supplying of only the nitrogen 408 is started. In addition, the supplying of the deionized water 409 to the treating bath 407 is stopped, and simultaneously, the deionized water 409 is discharged from the treating bath 407 through the discharge port 406, as shown in FIG. 2F.
After the deionized water 409 is discharged from the treating bath 407, the supplying of the nitrogen gas is stopped. At the same time, the hermetically sealed chamber 402 is evacuated by a vacuum pump (not shown) so that the hermetically sealed chamber 402 is put in a reduced pressure condition, as shown in FIG. 2G. The result is that the IPA on the surface of the wafer 401, which was substituted for the deionized water, is caused to evaporate, and therefore, the wafer 401 is dried.
After completion of the drying of the wafer 401, the supplying of the nitrogen gas 408 is, started. Thereafter, when a time of, for example, about 30 seconds has elapsed, the vacuum pump is stopped, so that the pressure in the hermetically sealed chamber 402 is restored from the reduced pressure condition to the pressure of the atmosphere, as shown in FIG. 2H.
After the pressure of the atmosphere is restored, the lid 403 is opened, and the wafer 401 is taken out.
In the above mentioned wafer etching and rinsing method, before the pulling-up of the wafer, the vapor of the organic solvent is blown against the rising stream of the deionized water. However, the deionized water is overflowed from the treating bath, and in addition, the water surface is heaving because of the rising stream of the deionized water, with the result that a uniform thick IPA layer can never be formed on the deionized water surface.
In addition, if the wafer is rinsed in the nitrogen atmosphere after the wet-process is carried out, even if the wafer is put in the rising water stream, since the deionized wafer water has a high surface tension, it is difficult to exhaust extremely fine particles of,for sample, not larger than 0.2 .mu.m in the proximity of the treating bath surface.
Furthermore, the particles remaining in the treating bath adhere to the wafer in succeeding processing.
The particles which could not be exhausted, prevent formation of the uniform organic solvent layer on the wafer surface. Accordingly, when the wafer surface has convex and concave areas in particular, when the wafer surface includes a hydrophobic surface and a hydrophilic surface, the deionized water is apt to remain at its boundary, and therefore, the particles are adhered. If the particles are adhered, water marks are generated because of moisture included in the particles. In the process for forming a hemispherical grained silicon (called a "HGS-Si"hereinafter) by utilizing a migration of a silicon film, which is now expected as the capacitor electrode of a highly integrated DRAM such as the 64 Mbit DRAM and a succeeding generation of DRAMs, an extremely fine remaining, water prevents the migration of a silicon film. The result is that such a large problem occurs that the capacitance value of the DRAM capacitor becomes small and the yield of production and the reliability are deteriorated.
In order to solve the above mentioned problems, it is necessary to sufficiently exhaust the particles at the time of rinsing the wafer after the wet-process, and to form a uniform and thick organic solvent layer.